The invention concerns a device for adjusting the rotational angle relationship of a camshaft to a drive wheel or element of an internal combustion engine.
An adjustment device for continuously adjusting the angular relationship of a camshaft for actuating gas exchange valves of an internal combustion engine relative to its drive element is known, comprising a servomotor which is actuated by a pressurized medium, in particular a hydraulic medium, and which has working chambers whose enclosed volumes can be increased or reduced by predetermined volume amounts during an adjustment.
In an adjustment device known from EP-A-0 163 046, two hydraulic servomotors are provided on a diameter of a part connected to the camshaft and each of these is equipped with a servopiston which acts via a roller on a ramp which is located on a drive gearwheel radially surrounding the part connected to the camshaft. The two servomotors are separately subjected to pressure and the pressure is controlled by separate valves. The servomotors are triggered by a valve arrangement in such a way that the outwardly moved piston of one servomotor is subjected to pressure and the working space of the other, opposite servomotor is relieved so that the piston of this servomotor can deflect following the ramp. In the case of uneven pressure in the servomotors, the servopiston is displaced and the roller acts both on the ramp of the drive wheel and on the shaft. This angular adjustment can take place in both directions.
Although the oil pressure source present in an internal combustion engine for lubrication purposes can be employed as the drive means for adjusting the camshaft, it only generates a relatively low pressure and is also limited with respect to the delivery volume per unit time. Furthermore, the additional pressurized medium consumption is substantial so that the use of a larger oil pressure source is necessary. A separate high pressure pump, on the other hand, requires more components and energy consumption. In addition, the device proposed is also complicated because two separate magnetic valves or a three-position valve must be employed in order to trigger the two servomotors.